All lovers of fermented foods - from yogurt to sourdough - enjoy the handiwork of yeast. These unicellular organisms live around us, floating through the air and resting on surfaces - waiting for an opportunity to start their lifecycle.
Apart from deciding what grapes to use in a wine, decisions around yeast are arguably some of the most important a producer will make.
What is wine yeast and how does it work?
Yeast are responsible for fermentation. Without yeast, you cannot make wine. They chow down on the grape juice’s sugar, converting it to alcohol, heat, and carbon dioxide (CO2). Winemakers have two fermentation options when deciding on yeast: cultured or native.
Cultured Wine Yeast.
Humans have been making wine for thousands of years, and over time they discovered that certain fermentation containers and wineries consistently made delicious wines. Particular strains of ambient yeast out-competed others. Scientific zymotechnology advances (the study of yeast fermentation) later isolated the dominant strains and reproduced them in the laboratory for commercial use. Today, winemakers have hundreds of options when it comes to commercially available yeast.
What does ‘Native Yeast’ mean on a bottle of wine?
Winemakers avoid adding cultured yeast to their grape juice if they want a native fermentation. The juice is left out and ambient yeast inoculate the wine naturally.
Interestingly, wineries with long production histories may not need to inoculate their wine tanks with commercial yeast strains. Ambient yeast floating around the facilities from decades or even centuries of winemaking will reliably ferment the new juice without any human intervention.
But there are risks with native fermentations. The winemaker doesn’t know what strain of yeast is going to dominate the fermentation process; some strains of yeast can create funky, off-aromas. However, purists argue that native yeast fashion more complex wines for this very reason.
Native fermentations may be unsuitable for every vintage. If the grapes come into the winery damaged, the winemaker may opt for a quick, clean fermentation by using a cultured yeast strain. Likewise, a winemaker can start out with the intention of doing a native fermentation, but if, for whatever reason, the fermentation doesn’t start, she will add a cultured yeast before the juice spoils.
How to choose which yeast to use?
Selecting yeast is serious business. Yeast manufacturers print specification charts that include a menu of choices. These charts are a lot like trip reservation websites: Do you want a hotel with complimentary breakfast? What about a pool? Do you need an airport shuttle? This gives winemakers an opportunity to prioritize different criteria based on the wine they’re trying to make.
Let’s look at a few of the major deciding factors.
Yeast and Alcohol.
Yeasts are incredibly sensitive to alcohol levels. One of the challenges in working with native yeast is that they tend to die off early in the fermentation process, leaving the wine open to possible microbial spoilage before the fermentation finishes.
Alternatively, scientists can select cultured yeast to survive high alcohol levels, but at around 14% ABV, even they have trouble. A winemaker who crafts a bold 15.5% ABV California Zinfandel will need to choose a yeast that can withstand this hostile environment.
Yeast and Temperature.
Another deciding factor is temperature sensitivity. If the winery is making a crisp Sauvignon Blanc in chilled fermentation tanks, then the yeast need to work in a cooler environment, maybe down to 55℉. Red wines require hotter fermentations to extract color, so selecting a yeast that can survive up to 90℉ will be important.
Other wineries may not have temperature controlled fermentation vessels. This means that the yeast has to live in whatever the ambient temperature of the winery happens to be around harvest time, whether it’s in Eastern Washington or Central California.
Yeast and Sensory Enhancements.
Beyond the technical specifications, winemakers select yeast to build a wine’s sensory profile. Yeast strains can change the flavor the wine, perhaps creating strong fruity characteristics, or enhancing mid-palate mouthfeel. The best wine yeast amplify the wine’s intended style. Here are some fun yeast descriptors:
Rich, very big and bold, well-rounded profile. Nice soft fruit character with dry crisp finish.
Encourages development of varietal fruit flavors, balanced by complex aromas.
Ideal for light, fruity red wines for early consumption.
Produces distinctive intense berry, graham cracker nose. Jammy, rich, very smooth complex profile, slightly vinous.
Mild toast and vanilla nose. Mild fruit profile with balanced depth and complexity. Very dry finish. Dry red and white wines.
With all of these possibilities, how do producers decide which yeast to use?
Part of the art and skill of winemaking is selecting strains to compliment and augment the fruit’s natural qualities. The good news is that winemakers aren’t necessarily limited to a single choice.
One strategy employs different yeast strains on several batches of the same wine that’s been divided up into separate fermentation vessels. Winemakers can later blend these batches together creating a unique and complex sensorial experience in a well-balanced wine.
Interested in learning more?
Pay attention to wine labels. Sometimes they include information about yeast strains, whether it’s a native fermentation or a cultured yeast. This can tell you a lot about the wine. Also, if you have the opportunity to speak with winemakers, ask them about yeast choices. It’s sure to lead to a passionate conversation!
If you want to discover a wide variety of wines and wine styles, join one of our 6 wine clubs, or shop in our online wine store! We feature wines using both cultured and native yeasts along with diverse fermentation techniques.
Author Bio: Erin O’Reilly is a Certified Specialist of Wine with the Society of Wine Educators and a long-time lover of all things fermented grape. She pens her work from Monterey wine country where she raises a glass to the growers and producers crafting wines that transcend time.